CharlesT is correct - it is very importnat to take the coverstock and the surface preparation into account. The are a unit with the core and its features.
Basically, a lower RG will rev up easier and also deliver its energy easier in the back end once it hits the dry and the core comes into its stable end position. This can help on long/heavier patterns. A higher RG will conserve the energy better and deliver it later, relatively. The RG differential will tell you much much flare potential a ball offers, and the amount of hook you can create through the pin placement. But how much it actually flares depends on the drilling, and how it reacts overall will more depend on the surface prep.
If you take both of your LM balls. drilled the same, I'd say you will recognize a difference, because the BPR's differential is a lot bigger than the BRB's. The RG differences will IMHO hardly matter. But with the same setup, the BPR should be better suited for more and longer oil than the BRB - while you have to keep in mind that the surface prep will do more on the condition suitablility than the pin position.

The pin is important to determine how much and when the ball will react, while the surface prep makes it suitable and working effectively on a certain condition - but it makes sense to fit both aspects into a good package to exploit a ball's potential (see also above for core specs).
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DizzyFugu - Reporting from Germany

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